Asymmetrically split charged coupled device

ABSTRACT

A charged coupled device is disclosed including an asymmetrical split with independent control over the regions on opposite sides of the split. The charge coupled device is configurable for use in multiline or kinetic spectroscopy, and includes two separate horizontal registers with optional charge dump regions for improving efficiency.

TECHNICAL FIELD

This invention relates to charge coupled devices, and more specifically,to an improved use of a charge coupled device including an asymmetricalsplit and for use primarily in spectroscopy applications. The inventivemethod and apparatus is useful in both kinetic spectroscopy andmultiline spectroscopy.

BACKGROUND OF THE INVENTION

Charged coupled devices (CCDs) have been in use for decades and are wellknown in the field of spectroscopy. Spectroscopy typically involvesilluminating one or more rows of a CCD with the spectrum of a signal andthen analyzing the captured spectrum represented by the varyingmagnitudes of charge which accumulate on the various elements of theCCD. For example, if one row of the CCD is used to capture the spectrum,the varying magnitudes of charge along the row represent the varyingamplitudes of different wavelengths which comprise the spectrum.

The use of CCDs in spectroscopy may be divided into at least two wellknown types: multiline spectroscopy and kinetic spectroscopy.Commercially available CCDs are usually extremely application specific,and typically are manufactured for use in either multiline spectroscopy,kinetic spectroscopy, or some other application. Conventional CCDsinclude little or no ability to adapt to different applications.

Kinetic spectroscopy involves obtaining multiple spectra, one at a time,at a relatively high rate, and then reading them from the CCD. FIG. 1shows a conceptual diagram of a CCD for use in kinetic spectroscopy. Thefirst row of elements 101 is utilized to capture a spectrum by focusingthe desired spectrum only on row 101. After the spectrum is captured atrow 101, it is shifted down to row 102 immediately below row 101 and thenext spectrum is captured at row 101. In one commercially available CCD,all rows except the top row 101 are masked. Thus, once the spectrum iscaptured and shifted down into row 102, it is no longer subject todistortion from unwanted light signals and the masked rows operateeffectively as a memory. Utilizing, for example, an off the shelf1024×256 CCD 100 of the type described, approximately 65,000 spectra persecond may be collected for subsequent read-out through horizontalregister 103 and amplifier 104.

Although the arrangement shown in FIG. 1 has been widely accepted in theprior art for performing kinetic spectroscopy, there are drawbacks tosuch an arrangement. First, since only one row of CCD elements istypically utilized to capture the spectrum, the device is not verysensitive. If the spectrum is focused on plural rows of CCD elements,the device will be more sensitive, however, the read out time willincrease dramatically since a spectrum occupying N rows of elements willrequire N times the read out time when compared with a spectrumoccupying one row. The slower read out time is unacceptable in certainapplications.

Another problem with the arrangement described is that it is relativelyinflexible. Specifically, the CCD with all of its rows except one maskedis not suitable for multiline spectroscopy, described below. Moreparticularly, multiline spectroscopy requires several spectra to becaptured simultaneously. The availability of only one row of unmaskedelements in the arrangement of FIG. 1 is unsuitable. Thus, if thespecific application changes, a whole new design is required.

In view of the above, it can be appreciated that there exists a need inthe art for a more sensitive CCD based device which is able to captureand read out spectra at a fast rate for use in kinetic spectroscopy, andwhich is flexible enough to be adapted for different uses.

Multiline spectroscopy is another branch of spectroscopy which is oftenimplemented using CCD devices. FIG. 2 shows a conceptual diagram of aCCD being utilized to effectuate multiline spectroscopy.

In multiline spectroscopy, several separate and distinct spectra arecaptured by a CCD and read out separately for analysis throughhorizontal shift register 210. The plural spectra are usually capturedsimultaneously, and then later shifted out of the CCD sequentially forstorage and analysis. The arrangement in FIG. 2 includes such a chargecoupled device 200, a plurality of exemplary spectra represented by 201through 204, and a horizontal register 210 for reading out the spectra.Additionally, the regions 205 through 208 represent separation bands inorder to prevent energy from each distinct spectrum from contaminatingthe energy in the regions storing the other spectra.

In operation, the spectra are first captured on the CCD 200, perhapswith the use of a mechanical shutter. Next, the spectra are read byplacing them into horizontal register 210 and then shifting eachspectrum from register 210 for later storage, analysis or any otherrequired processing.

A problem with the use of arrangements such as that of FIG. 2 toaccomplish multiline spectroscopy is that the dark bands 205 through 208must be independently read into horizontal register 210 and shifted out.Accordingly, the overall operation of the device is much slower thandesirable.

Another problem with the arrangement of FIG. 2 for multilinespectroscopy is that if it is desired to utilize the same chip forkinetic spectroscopy, a large waste in space and time results.Specifically, FIG. 6 shows a conventional CCD device 601 and includes arepresentation 602 of a single spectrum stored in one row of the device.In operation, the spectrum 602 is transferred into horizontal register603 for shifting out. The dark charge from region 603 must then also beshifted out. This results in wasted time and thus, slower throughout.

Alternatively, when a device is being utilized to capture singlespectrum using the technique described, an arrangement such as thatshown in FIG. 7 may be used. The arrangement of FIG. 7 includes arelatively small CCD for capturing a single spectrum and a horizontalregister 702 for the read out of such spectrum. However, if it is laterdesired to do multiline spectroscopy utilizing a larger CCD device, theentire chip would have to be replaced.

In view of the above there exists a need in the art for an improved CCDarrangement for performing multiline and kinetic spectroscopy.Additionally, such device should be adaptable easily for either of theforegoing types of spectroscopy and should be efficient when operated ineither mode. Finally, there exists a need for improved speed whenperforming either type of spectroscopy utilizing CCD devices.

SUMMARY OF THE INVENTION

The above and other problems of the prior art are overcome and atechnical advance is achieved in accordance with the present inventionwhich relates to an improved charge coupled device (CCD) which includesan asymmetrical split, independent control over the regions on each sideof the asymmetrical split, and two horizontal registers for readinginformation from the CCD. The horizontal registers, one on each side ofthe CCD, are also independently controllable like the shifting on eachside of the asymmetrical split.

In operation, the device may be used for kinetic spectroscopy or formultiline spectroscopy. In either case, a spectrometer, for example, ispreferably utilized to capture light, split it into its spectrum, andconvey the spectrum to the CCD.

When utilized for kinetic spectroscopy, a single spectrum may occupymultiple rows of elements, thereby increasing sensitivity over prior artsingle row spectroscopy devices. Unlike the prior art however,unacceptable additional read out time is not required because thespectra may be binned at the asymmetrical split, a technique onlypossible due to the independent control of the regions of the CCD onopposite sides of the split.

The inventive device is also capable of rapidly transferringsequentially acquired spectra to a horizontal register for read outwhile independently transferring dark charge, in the opposite direction,to a different horizontal register. Accordingly, when operating in thekinetic spectroscopy mode, charge in the relatively small region on oneside of the asymmetrical split is shifted in the opposite direction fromthe dark charge on the other side of the asymmetrical split. Theadditional time required to read out the dark charge through thehorizontal register is thus avoided, as any dark charge is read outsubstantially simultaneous with the reading out of the capturedspectrum.

When it is desirable to use the inventive device in the multilinespectroscopy mode, plural spectra are captured in the relatively largeregion of the CCD on one side of the asymmetrical split and binned intoa smaller number of rows on the relatively smaller side of theasymmetrical split. The binning is done such that (i) the averagebinning rate is equal to the ratio of the number of rows in therelatively larger region of the CCD divided by the number of rows in therelatively smaller region of the CCD, and (ii) the separation bands ofdark charge are binned into separate rows from those into which spectraare binned. This allows for multiple row spectra, relatively quick readout, and easy configurability of the CCD to be used efficiently for bothmultiline and kinetic spectroscopy.

For purposes herein, an asymmetrically split CCD is a CCD wherein theregion controllable on one side of said split is at least twenty percentlarger than the region on the other side thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art CCD arranged to implement kinetic spectroscopy;

FIG. 2 shows a prior art CCD arranged to implement multilinespectroscopy;

FIG. 3 shows an asymmetrically split CCD device in accordance with thepresent invention;

FIG. 4 shows the asymmetrically split CCD device of FIG. 3 when utilizedin the multiline spectroscopy mode;

FIG. 5 shows an exploded view of a portion of the CCD device of FIG. 3;

FIG. 6 shows an example of the prior art CCD device being used tocapture a single spectrum;

FIG. 7 shows an additional prior art CCD device capturing a singlespectrum; and

FIG. 8 shows a conceptual view of the inventive apparatus when used in amode for performing kinetic spectroscopy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows a representation of an exemplary embodiment of the presentinvention comprising a 1340×400 CCD. The arrangement of FIG. 3 includesa novel CCD 300 including a relatively large lower region 301 and arelatively smaller upper region 302 separated by a split 303. The split303 may be located for example, such that there are 80 rows above it and320 of the 400 rows below it, with each of the regions 302 and 301 beingcontrollable independently of each other. Specifically, rows of chargeon one side of split 303 may be shifted up or down independently of rowsof charge on the other side of split 303. Additionally, rows of chargemay be shifted across asymmetrical split 303.

While the 320 to 80 ratio in the example of FIG. 3 represents but oneworkable example, other asymmetrically split arrangements are possible.Importantly, the split is such that the small region 302 is suitable forkinetic spectroscopy while the larger region 301 is suitable formultiline spectroscopy.

The CCD 300 includes two horizontal registers 304 and 305 for readingcharge from the CCD 300 independently of one another. One or both ofhorizontal registers 304 and 305 may include a charge dump area 306 forproviding parallel dump of all charge within horizontal register 304 or305 as the case may be. Techniques for manufacturing such charge dumpsare known in the art and will not be described in detail herein.

The operation of the novel device will first be described in its modefor utilization in performing multiline spectroscopy. In operation ofmultiline spectroscopy, a plurality of spectra are placed in region 301,each separated by bands of dark charge in order to prevent interferencecaused by energy from one spectrum spilling over into another spectrum.FIG. 4 shows a conceptual representation of the device of FIG. 3,utilized in its multiline spectroscopy mode including a plurality ofexemplary spectra 401 through 404 included thereon. Spectra 401 through404 are separated by regions 405 in order to prevent contamination ofenergy from one spectra to another.

For purposes of explanation, we presume that region 302 comprises eightyrows, and region 301 comprises 320 rows. Since the 320 rows of chargefrom region 301 are to be placed into region 302, there is a desire toprovide for 4 to 1 binning at split 303. Moreover, we presume that eachof spectra 401 through 404 is eight rows high, and that region 405 iseight rows as well.

In order to shift out the multiple spectra, the four rows 405a arebinned into row 406, the first row above the split 303. The row 406would then be shifted one row upward, thereby allowing the binning ofthe next four rows of dark charge from region 405a into row 406. Theprocess continues to repeat itself in a similar manner such that eachset of four rows from region 301 is binned into one row in region 302.Since both the light and dark alternating areas in region 301 are eightrows high, the resulting arrangement in region 302 would be (i) two rowsof a spectrum comprising four binned rows of spectra from below 301, and(ii) two rows comprising dark charge.

FIG. 5 shows an exploded view of region 302 of the CCD device of FIG. 4after the operation of the binning at the asymmetrical split describedabove. Each of the rows 501 and 502 include four rows of dark chargefrom region 301 of the device, and rows 503 and 504 contain thespectrum. The alternating pattern repeats itself as shown in FIG. 5.

The binned spectra in rows 503 and 504 may then be read out throughhorizontal register 304. It is also contemplated that an 8 to 1 binningmay be used in the foregoing example if the capacity of each CCD elementis large enough to hold all required charge.

It can be appreciated from the foregoing that the implementation ofmultiline spectroscopy utilizing the foregoing arrangement allows formore sensitive spectra to be obtained by providing for multiple rowspectrum yet the time required to read out such spectra is minimized dueto the binning occurring at asymmetrical split 303.

In a further embodiment, the dark charge from rows 501 and 502 may bequickly eliminated from horizontal register 304. Specifically, improvedspeed may be achieved by utilizing the charge dump 306 to eliminate theentire dark charge from register 304 in parallel without reading itserially out of horizontal register 304.

It is noted that the binning at the asymmetrical split may notnecessarily be constant and need not necessarily divide evenly into thedifferent rows of dark charge and spectra contained in region 301. Forexample, consider a situation in which the spectra each occupy ten rowsand the dark bands therebetween occupy ten rows. If the binning is stilldesired to be four to one, binning at the asymmetrical split should bedone such that the average ratio of rows in region 301 to rows in region302 is four to one. Additionally, the averaging should be done such thatdark charge rows are not mixed with the rows representing spectra.

In the foregoing example, a four to one binning ratio can be used tocompress 320 rows in region 301 into 80 rows in region 302 by anarrangement which bins according to the following algorithm: 5 to 1, 5to 1, 4 to 1, 4 to 1, 2 to 1, 5 to 1, 5 to 1, 4 to 1, 4 to 1, 2 to 1,repeat, etc. In accordance with the foregoing arrangement, the first 10rows would be binned into two rows of dark charge, and next 10 rowswould be binned into three rows of spectrum. Thus, the system providesfor efficient multiline spectroscopy by binning, at an asymmetricalsplit, in such a manner that (i) dark charge and spectra are separatedand (ii) the average binning ratio is equal to number of rows in therelatively large portion of the CCD divided by the number of rows in therelatively smaller portion of the CCD.

In another embodiment of the present invention, the arrangement of FIG.3 can be utilized to accomplish kinetic spectroscopy efficiently.Specifically, with reference to FIG. 3, the regions 302 may be utilizedto capture a spectrum, and such spectrum may be read out throughregister 304. However, the remaining dark charge need not be read outsince the dark charge in region 301 may be separately controlled andread out through register 305. FIG. 8 shows a conceptual representationof the use of the asymmetrically split CCD utilized to sequentially readout numerous spectra stored in the small region 302 while shifting darkcharge out of large region 301. The arrows indicate the direction ofcharge movement, and the dark charge may be dumped in charge dump 801.

In still another embodiment, kinetic spectroscopy may be accomplished bycapturing a single spectrum comprising multiple rows in region 302,binning such multiple row spectrum into one or more rows in region 301,and then capturing a subsequent spectrum in region 302. Thus, pluralspectra can be captured sequentially and rapidly, and each one binnedinto one or more rows in a larger region 301 wherein no light isincident.

The device shown in FIG. 3 may be utilized for multiline spectroscopy aspreviously described, as well as for kinetic spectroscopy by simplycontrolling it differently. Specifically, in the case where multilinespectroscopy is desired, the spectra are captured in region 301, binnedinto region 302, and read out through register 306. On the other hand,when kinetic spectroscopy is desired, the spectra to be analyzed arecaptured one at a time using plural rows in region 302, and read outthrough register 304 while the dark charge is dumped through register305.

By having the ability to shift charge on opposite sides of theasymmetrical split in opposite directions, the larger region of darkcharge can be dumped or shifted out through a different register thanthe spectra, as shown in FIG. 8. Additionally, the device can beconfigured to operate as a multiline spectroscopy device or a kineticspectroscopy device by simply using different control software.

While the foregoing describes the preferred embodiment of the invention,it is understood that various enhancements or other embodiments will beapparent to those of skill in the art. These variations are intended tobe covered by the following claims.

I claim:
 1. A method of performing multiline spectroscopy comprising thesteps of:configuring a charge coupled device with an asymmetrical split;capturing spectra in a first region of said charge coupled device whichis on one side of said asymmetrical split and which is relatively largerthen a second region on a second side of said asymmetrical split;binning, at said asymmetrical split, plural spectra into rows ofelements located on said second side of said asymmetrical split; andshifting said binned rows out of said charged coupled device through ahorizontal register.
 2. The method of claim 1 wherein said step ofbinning comprises binning dark charge into rows separate from rows intowhich spectra are binned.
 3. The method of claim 2 wherein the binningratio is equal to, on average, the number of rows in the first region ofsaid charge coupled device divided by the number of rows in the secondregion of said device.
 4. A method of binning charge in a charge coupleddevice having an asymmetrical split, the charge to be binnedrepresenting spectra and rows of dark charge, the method comprising thesteps of:binning the rows of spectra from a relatively large firstregion of said charge coupled device on one side of said asymmetricalsplit to a relatively small second region of said charge coupled deviceon another side of said asymmetrical split; and adapting said binningsuch that the average binning ratio is equal to the number of rows insaid first region divided by the number of rows is said second region,the binning ratio during at least one binning operation being differentthan the average binning ratio, the binning being accomplished such thatdark charge is kept separate from spectra.
 5. A method of performingspectroscopy comprising:providing a charge coupled device having anasymmetrical split, a first region on a first side of said split, and asecond region on a second side of said split; transmitting to saidcharge coupled device a signal indicative of which one of several typesof spectroscopy is desired; in response to said signal, binning chargefrom said first region to said second region if said signal indicates afirst type of spectroscopy is desired, and binning charge from saidsecond region to said first region if said signal indicates a secondtype of spectroscopy is desired.
 6. The method of claim 5 wherein saidfirst type of spectroscopy is multiline spectroscopy and said secondtype of spectroscopy is kinetic spectroscopy.
 7. A method of performingkinetic spectroscopy utilizing a spectrometer and an asymmetricallysplit charge coupled device, said asymmetrically split charge coupleddevice having a small region on one side of said asymmetrical split anda large region on an opposite side of said asymmetrical split, saidmethod comprising:capturing plural spectra, one at a time andsequentially, in said small region; subsequent to capturing eachspectrum, shifting charge representative of said spectrum in said smallregion out through a first shift register and shifting dark charge fromsaid large region out through a second shift register.